Computer systems output data to a variety of output devices, including printers, plotters, and computer controlled machines, such as a manufacturing machines. The operating system of the computer is assigned the task of interfacing with these peripheral hardware products so that the appropriate communications protocol and appropriate set of instructions are used by the computer to communicate with the peripheral. Because it is impractical to provide an interface for every device, the operating system provides a standard interface with a given functionality. Each peripheral then uses a device driver to interface with the standard interface of the operating system. The operating system thus controls each peripheral indirectly through the driver.
A goal of the operating system is to provide an application program environment which is independent of the output device used. A graphics device interface (GDI) achieves this goal. The GDI, typically part of the operating system, provides a defined set of functions. Each program, then, outputs its data by using these predefined functions. A peripheral driver translates these functions into a stream of commands to control the particular peripheral for which the driver was designed. The GDI, therefore, acts as a common denominator: the application programs translate their data into GDI functions and the drivers then translate these functions into peripheral commands. The net result is that the peripheral produces output resembling the image the application created on the computer.
Because device drivers were designed to operate a particular device, each peripheral required its own driver. For example, once a user connected a printer to the computer, the user would have find the correct printer driver to operate the printer and translate the image which the computer sought to print into a series of commands for that printer. Installing a printer driver is not a simple task for the user. In order to install the correct driver, and configure it properly, the user is often required to answer detailed questions about both the printer and the computer. For example, the user will have to identify the printer and determine which options are installed on the printer. Such information is not immediately apparent to the user, and thus often requires the user to seek assistance. Should the user enter the wrong information, the incorrect printer driver could be installed, or the correct printer driver could be installed incorrectly. In either case, the user will not have access to all of the functionality of the printer, and may not be able to print at all.
In an effort to simplify the process for users, the operating system of the computer will often contain pre-installed printer drivers for a variety of common printers. Thus, if the user seeks to connect one of the supported printers, the process becomes simplified: the user need only select the printer driver with the same name as the printer. However, this system does not provide any assistance to the user who wishes to use a printer which is not supported by the pre-installed printer drivers. Additionally, because printer options may change between the time that the drivers are incorporated into the operating system and the time the user buys the printer, it is not possible to create printer drivers ex ante which can support all of the options on the user's printer. The result is that, while the correct printer driver may already be installed on the computer, it is not configured to provide access to that printer's newest options.
In an effort to conserve memory on the computer, and thus provide additional, pre-installed printer drivers, a system was developed whereby a driver, called a universal printer driver, or unidriver, contained the vast majority of common printer driver code. Smaller drivers could then be written, using the functionality of the unidriver to control the printer. These smaller drivers, called minidrivers, together with the one unidriver, occupied significantly less computer memory storage than the separate printer drivers they replaced. As a result, a larger number of the minidrivers could be pre-installed with the operating system, lessening the chance that the user's printer would be an unsupported printer.
However, the unidriver-minidriver system did not provide any mechanism by which new functions and printers could be added. New features of printers could not be supported, even if a specific minidriver was written, because the unidriver did not have anywhere this new function could be mapped. Thus, new printer functions could only be added with a new version of the operating system, which contained a new unidriver.
In an effort to provide a more extensible unidriver-minidriver system, a new printer description format called the Generic Printer Description (GPD) was created. The GPD was a text-based printer description format, allowing for easier coding, providing greater human readability, and providing extensibility. The GPD file described all of the features on a printer and how to display those features to the user, and instruct the printer to perform those features. An updated unidriver was also created, which would parse the GPD file and present the options to the user. Thus, new functionality could be added without the need to rewrite the entire unidriver.
Despite the increased simplicity, and efficiency of the unidriver-GPD system, the user is still required to know which GPD file is appropriate for the printer the user seeks to attach to the system. This may be especially difficult in large corporations with a myriad of printers, or institutions where a network administrator may keep all of the disks which shipped with the printer and contained the appropriate GPD file. Even if the user has access to the GPD files, such as through the manufacturer's Internet web site, the user may not know which files are appropriate for the particular printer to which the user is attempting to print.